Index pulse generating circuit



May 24, 1949. w. L. GAINES 2,471,268

INDEX PULSE GENERATING CIRCUIT Filed May 22, 1945 SUMM/IVG 42 AMPLIFIER i INVENTQOR By W. L. GAl/VES I W 5 W A TTORNE) Patented May 24, 1949 rem-TENT IND EX PULSE GEN ERATIN G" CIRGUIT wWilbur L. Gaines,- Great Neck, Na rassignor .to Bell Telephone Laboratories,- -I'nc orporat,ed;;.-New York, N. Y., a corporation of New York Application May 22, 1945, serial-Nor595i2l0 4 Claims.

' This invention relates to control circuits. More particularly itrelatestozelectrical circuits adapt- -ecl to produce .xunidirectional electrical index pulses at theinstEmt a-device varying in either passesithr'ough arp'redetermined position in said wzr-ange, the position at%which pulses are produced being determined by adjustment of an electrical control device, the adjustable range of which suf- .fices to select any position through which the- 11",.V8iI'YlI1g. device-passes as that at which the index .xpulsesare produced.

' A principalobject of the invention is, accordxingly, tO-prOVide arr-electrical circuit which pro-- duces unidirectional electrical index pulses whene;

- ever avarying device passes through a predetermined/position.

' Other and further object of the inventionwill -becomeapparentduring the course of theiollowing description ofan-illustrative embodiment and from the appended claims.

- A- frequent-problem encountered in connection -.with object detecting and ranging systems, par-- ticularly with those employingradio energy which is directed in awsharp. .beam from an. antenna, wthe antenna being rotated in azimuth to scan "an area, is thatof providing a mark-on .theindicator oflthe radar .system at the instant the antenna-beam is directed in a particular preselected @direction. -The problem is more complex where, as is frequentlythe case,v the antenna is not rotate continuously but is oscillated back and forth through an arc to-coveronly a sector or portion ofvthe area which would. be covered by complete rotation of the antenna.

A convenient means of providing an electrical voltage the value of which at each instant represents theangle at which the antenna is directed is a circular potentiometer," across the Winding of which a source of "direct current voltage has been connected; the contact arm of which is turned in synchronism with the "turning motion of the antenna. If theantenna is oscillated back and forth" through anarc or sector, as is frequently desirable, the voltage alternately rises and falls between two-limiting values representing the range of" angles within theselected arcor sector. If-then-itisdesired to produce an azimuthmarkerpulse eachtime the antenna passes l through a particularangular direction Within the selectedarc-orsector, it is necessary to-devise a type of electrical-circuit which will produce pulse the voltage passes in either direction through:the-value -corresponding to that particular angular direction or azimuth.

direction over a prescribed. range of positions .552 I: lniiarrangementspofltherinvention this is accomplished;by'aprovidlng.;arzsecond manually ad- J'ustable.cnotentiometerzs 3.011055'4'Whi0h a second source of @directacurrent potential ofopposite po- 5 .larity isqconnected sathat .:a-.voltage equal to the -11 value. .corresponding;=.tosanym particulardesired directionv within: the: rangeiof: interest can be .1;established-bysmanualadjustment; (The second potentiometer;canaobviously be provided With a scale calibrated to read directly the angular dil rection corresponding to each setting.) The voltage\thus estahlishectand:thevaryingvoltage from r-r the;potentiometemassociated :wviththe antenna are'intrOdHCBdintO aiconventionalfsumming am- 15 ;plifieri=i. zeramamplifier whose. output represents the lsumof two or:mora input voltages. If one input voltage is made'totvary-ima negative sense with:respect.torgroundzand the sother in a posi- ;tive. sense..- athenteachntime; the varying voltage lpassesrthrouglnthe azalue; corresponding to the .1 setting of; the anamiallyfadjusted potentiometer the sum oicthertwoyoltagessand the output of the summingramplifienwilllpasszthrough zero at the .preselected point:tritmemainsathen only to pro- 5- Vida ani electricakcircuit whichwill produce index pulses of.thedesiredcharacter;each.time the output of the isummingamplifienpasses through zero. IThis'lattersrequirement'dshomplicated' by the fact :that: the::variablei-ivoltagemcan"v bexeither increasing. or. decreasing asritapasses through thecritical 1; .value's. and"; :thecirrventiohntherefore comprises a circuitwhich Williprovidethedesiredindex pulses rior either.:direction ofi variation.

I :The' principles ointheainvention:lwillbecome more :readilyapparent irom thefollowing descripxution ofian'illustrativercircuit :of the invention and 1 rfromithe-accompanying:drawings in which:

. 1 cFig; l1; shows incschematic::diagram .iorm the .-..generali arrangement;and-illustratesa. .use of an 40. .illustrativefembodiment oitheinvention; and

:Fig. .2 shows inselectricalw schematic. diagram formthetparticularicifcuitsremployed in an illusr ;:.trative emb'odimenti'ofi the-invention.

lnimoreidetaillirc Eig. inclement: it :represents 45. a dipole;- 01'. thei like, antenna; positioned at the focus of 2a .parabol oidalrreflecting.member' l 2, the combination:ibeingasupported; on atvertical shaft Mr-arranged tDiibE rotatedrcontinuously or oscil- -...lated backzandcfnrthlthrough an are by. motor -mechanism: IBJJ: Alternatively-:nrotor mechanism l6 canvbe. deenergizedzand: thezzshaft can be ro- .;..tated orsoscillated byzhandwheel-ld 1' The :lower endtoiishafit- Mz turns :awccntacting :xxme-mbe'r Zllawhich itraverse's; theuwindinglii of a circular potentiometer; one. end of-which winding is grounded and the other end of which connects to the negative terminal of a direct current potential source 22 supplying a suitable voltage such as 200 volts. The positive terminal of source 22 is grounded as shown.

There is also provided a second circular potentiometer, which can conveniently be substantially identical with the above-mentioned potentiometer, having winding 28 and contacting member 30, the latter member being manually adjustable to any desired position on the winding 28. One end of winding 28 is grounded and the other end connects to the positive terminal of a second suitable direct current potential source 26, having a voltage of 200 volts. The negative terminal of source 26 is grounded.

The contacting arms 20 and 30 of the two above-mentioned potentiometers are connected to input terminals of summing amplifier 34, a conventional form of which is shown in detail in Fig. 2, (vacuum tubes V1 and V2 and associated circuits) to be described in detail hereinunder.

The output of the summing amplifier 34, which is, of course, equal at any instant to the sum of the voltages applied to the input terminals thereof, is connected to the pulse generator 36, a suitable form of which is also shown in detail in Fig. 2, vacuum tubes V3 to V6, inclusive, and associated circuits to be described in detail presently.

Pulse generator 36 responds to the output of amplifier 34 by providing at terminals 38 and 40 a positive pulse and a negative pulse, respectively, whenever the output of amplifier 34 passes through zero weather its voltage is passing from negative to positive values with respect to zero (or ground) or vice versa.

Since one input voltage from source 22 is negative with respect to ground and the other from source 26 is positive with respect to ground, the input to amplifier 34 will pass through zero as contacting member 20 passes the point on winding I8 corresponding to the point on winding 28 at which contacting member 30 is set. Also, where the voltage derived from source 22 through winding 18 is greater than that derived from source 26 through winding 28 the sum of the inputs to amplifier 34 will be negative with respect to ground and. for the reverse condition the sum of the inputs will be positive so that in passing through zero the sign of the output voltage of amplifier 34 will change. The direction of the change, i. e. whether from positive to negative or vice versa, obviously depends upon the direction in which shaft [4 is being turned.

In Fig. 2, as pointed out above, vacuum tubes V1 and V2 and the circuits directly associated therewith, comprise a conventional form of summing amplifier which comprises two stages, the first including vacuum tube V1 which is in reality the summing amplifier stage and the second including vacuum tube V2 which is essentially an amplifier stage, The output of this amplifier, from anode 5 of tube V2, varies in the same way as the algebraic sum of the two input voltages, passing through zero when the sum is zero.

The input terminals 200 and 204 are connected to two series resistors 202 and 206 which, together with the common shunt resistor 208, determine the portions of the two input voltages (from potentiometer contact arms 20 and 30 of Fig. 1) which are applied to the control element or grid l of vacuum tube V1. As is well known to those skilled in the art, the input series resistors 20.2 and 206 can be given'different values when a conditioned summation of the two input voltages is desired, i. e. if it were desired to vary the manually controlled voltage over a greater or lesser range than the voltage controlled by the scanning member, its effect upon the input of the summing amplifier could be brought back to a parity relation with the latter voltage by properly proportioning resistors 202 and 206 with respect to each other. As this is not important in the illustrative embodiment selected, it is assumed for the sake of simplicity that the range of variation is the same for both voltages in which case resistors 202 and 205 can be of the same value. The matter is mentioned only for the purpose of pointing out that numerous equivalent arrangements can be introduced into systems of the invention at many points thereof without departure from the spirit and scope of the invention.

Tube V1 as shown in Fig. 2, can conveniently be a double triode in a single envelope, or it can equally well be two separate triode vacuum tubes. The cathode elements 3 and 6 of tube V1 are connected together as shown and by means of the common cathode resistor 2l4 are connected to the 200 volt terminal of a suitable source of direct current potential the positive terminal of which is grounded.

One of the plates or anodes, designated 2. of tube V1 is connected to terminal 280 which in turn is connected for normal operation to the positive terminal of a suitable source of volts direct current, the negative terminal of the source being rounded. The heater elements for the cathodes 3 and 0 of V1 are also connected through resistors H0 and H2 to terminal 280 as shown for the purpose of reducing the introduction of power frequency noise into the amplifier. The other anode 5 of tube V1 connects through resistor 222 to terminal 282 to which is connected for normal operation to the positive terminal of a suitable source of 200 volts direct current, the negative terminal of the source being grounded. Resistors 216 and 2|8 provide at their junction point a suitable bias potential for grid 4 of tube V1, the other ends of resistors 216 and 2 l8 being connected, respectively, to ground and to 200 volts direct current normally on terminal 218. Resistor 220 connecting the anode 5 and grid 4 of tube V1 provides a stabilizing feedback voltage.

The first half of tube V1 comprising anode 2, control grid 1 and cathode 3 is virtually a cathode follower stage since the second half comprisin anode 5, control grid 4 and cathode 6 is coupled thereto only through the common cathode resistor 2M. The latter resistor also, of course, serves to feed back energy from the second half to the first and thus stabilizes the action of the amplifier particularly against variation in the voltages of the supply sources mentioned above.

It can be readily seen that a multistage direct coupled amplifier of this type would require a rather high voltage power supply if some precautions were not taken. Such precautions have been taken in this circuit and the operating point of each tube is kept within reasonable limits by means of the negative supply and potential dividers. Resistors 236 and 242 represent such dividers. The negative supply also permits the operation of such a circuit as shown in V1 with its grids substantially at ground potential. This circuit needs a large common cathode resistance for effective operation and to provide the necess'ary;'voltageoforathei: curr IItJ-ZflOWz; in thisrresiste quently ithe: potential .of anodenZz will :decrease ance; anegatvie; sup.ply .ls -.required.i Also;;the voltage drop across cathode .IGSlStOIJZIA.

Thecoutput fromt'ianodeei't of tube Vreonnects; williiincrease.rendering:control:grid AzofxtubeNrr; directly to the; controlcgridil ;of; tub'eNz; Tube efliectivelyymoreznegative; decreasing; the. current" V2, like tube V1, can conveniently be a doubleitrie throi-lghzt-h'evanode- 5:, cathode; 6=3-path:.ofitube-Va,-; odewithin asingle envelope; the first half thereand.-the-;potential1:ofianode :5 of :tube V3 w1ll'.con+. ofcomprising anode, 2; controlagrid;hand cathe sequently increase. Obviouslyif the IIIDLltVOItJ-iode -43 andathea:secondzhalt:comprisingianoder.5, age is then brought back-to zer o,'.thes-potentialsl1.; controlqgrid '41 d cathodes- ,401; alternatively, of anodes 2 and 5 of tuber-Vs'yvill ret-urn-tovthelrc two separateytriode .tubes...-can;bei; employed: .5 original-equalp tentials. If the: inpu 'v l gei-is Like tube V1 thertwolhalveszcf tube .Vzarecounext increasedgin a negative: direction; the pos, pled through a. m np athod eresistorcpath:. tential: of anode-2 oftube V3 will 1ncrease;de-: w comprising ,resistorscnfiz;and12281but an iaddi-i, creasing fi esbias across cathode resistor; 24kt tional bias in this: pathilis .provided. through: rer nd ringcon r l erid'i of :tube V3 more posi iv sistor- 230 which;connects between-the junction gi 'fi ing the currentrinthe cathodet; .anodel point of resistors .1226:and.228candillterminalilzl8, pathoi tube V3 and causing; the potential; of anode.

to which, as hereinbefore describedaiszconnected 5 to decrease. Again if the input voltageafnegaw the negative;termmal,. of a suitable source .of.200 tivel. is brought back'to zero, the pot l voit mr t nt, anodes Land 5 0i tuberVs' will-ireturn; toztheir:

Anode-2 oftubeNz.connects directlytoterminal -fi v0f ity- 282 "(normally atr+200:voltsidirectcurrent) and ThemeXt Stage, lncludlng VacuumtubeW. 1s .a

anode iof tube V2 connects through -resistor 232" m l m u cathodefonower Stage to terminal=212 which;isznormally connected:to n e ri s-l and-'4 areiconnected as shownsto-i the positive terminal of aasuitablmsource of 360 anodes-2 d- 3 P y. Od volts direct-current,- thenegative-terminalof the 2 ndz- 0f ube V i-are connectedto terminal 212::

sourceloeing groundedc'. (+360 voltsrdirectcurrent) as shown.v Cathodes The control rid dobtains :a:bias.fr'om the com- 3-and 6. of tuberVi connect through-individua binationof potentiometeri236 ancl' fixednresistors cat resistors 5 a d 258, sp tiv y, t 234 and 238, whichthree.resistivezelements are ground. :As me abov feedback-voltage connected in series as. shownibetween: terminal aoi pr d'f om hode 6 0f tubevi to control 212 (+360 volts) and.:.ground;. :Adjustment of grid- 4--of tube'V th o res stor 56.-

this bias. is afiorded=byi potentiometer. 236, as As is Well known to those 'skilledlin .the .art, a:

shown, cathode follower stage: of the type-includingtube-- A feedback voltage is,also-supplied.toigrid 4 of V4 functionstoreproduce. across-its. respective tube V2 through tubesqVz andizvilanduthe circuitcathoderesistorsthe voltage wave formsdevel including resistor 256-for the :purpose of stabilizoped at the. outputs of the immediately preceding ingthe gain and operating pointof the amplifier. i stage but-at-a lower impedance level..

The stage includingztube .-V2 is-employedpri- The remainder ofthe' circuitof Fig.- 2," inc1ud 4 marily for the 13111130861 01. amplification of the ng double diode vacuumptube Vs-v and double voltage provide atanodei .of;tube .-V1.'- 40 triode;:vacuumtube Vs, ,will be considered as a The next stagewincluding tubevVs'is a-substanunits. tially conventional cathode-coupled phase-in- The voltage developed acrosscathode resistor-- verter stage. Tube VHS,as;.'shoWn, a-d0ub1-tri- 254,-above-mentioned, is'connectedr'through reode, control grid of which connects to the outsistor26l :to anode 5v of tube V5 and control grid put anode 5 of tube V2 ,through' th circuit .in- 4 oftube V6.- Resistor 26! is shunted byresistors eluding potentiometer 242'iand-cresistor:24'0in se-= 252 and 263 connectedini series, thedunction ries, theupper endtof potentiometer. 242 conpoint ofthe lasttwo resistors being connected necting to anode 5 of-tubeiV'zrandathelowe end to cathode 4-01 tubeVs, andcontrol .grid l-of of-resistor 240 connectin toeterminal2 l8 (200 tubeV-c; as shown.

volts direct current). The voltage developed across cathode resistor Cathodes 3 and 6 of tubelva are connected to- 258;,inadd-itionto being fed backthrough resistor gether as shown and through. the common cath- 256 .to control-grid :4 of tube V2 asde-scribed above; ode resistor 244 to ground; 5 is also directlyimpressed upon cathode 8 and 1 Anodes 2"and5' oftuberzVa connect through anode a-oftube V5 equal isolating resistors-246 and 248 respectively,- 55* With no input voltage to the control igrid' l of to terminal212 (+360 volts direct current). tubewl/ai-ite. for thezero voltageinput condition-i The control grid4 of tube Va is provided'with a to the summing amplifier (tubes'Vi' and V2), the substantially constantbiaspvoltageby beingconvoltages; developed across the: Cal'IhOdBuIBSiStOIS nected to therjunctionofresistorsu250 and 252. 25 lIand-258 associated with tube V4 will beequalp These resistors are connectediinrseries; the -up- -i.' e. their-difference will be zero. The; biases .iap-fi. per terminal of resistor 250::being connected to pliedtotube-Ve are such thatin passing: throughw terminal 212 (+360 volts direct-current) andithethe-condition-of zero difference between the volts:v lower terminal of resistor.252%,beingigrounded. ages acrosszresistors 254 and258-in-either direce;

The phase-inverter stage including tube-"Va is tion,v e. from positive to negative, or vice versa, adjusted by means of potentiometerl242 sothat voltage, pulseswill be generated at anodes! and with noinputvoltagetfromaanode ion-tube -V2 55v of'tube V6, graphically represented by pulses. applied to controlgridel; the :anodeacathode cur 29llgandqz92t in 155g. 2, respectively; pulse290-at; rents between-anode.2iandccathodefiiiandanode anode'2 'b'eing positive and pulse 292 at anodex5- 5 and cathodedot tubewVa willbeaequal-m The po being negative. tentials. at anodes 2--and:;5 sofrtubei V3 areathen This isibrought about in the following manner. equalwthat s, therea iSf\zerospotential sdifirence Assume. that cathodei3 .oftube'V4 is positive with: between .them. If ;.then-j;:a,; voltagesincreasing in-a; respect to. cathode 6-0f tube V4 and that the volt positive vdirection is ZrDDlifidGtOlCOHllIQL glid'" ot ages of these two cathodesareapproachingtheir; tubemvs; the; c rr nt thmuglti he nod atli common zero input value.- The. positive --voltodee3,-pa;th .oiitubewvsiwllt increaseeandi conee age at'cathode 3* finds a path through resistor 262 to make control grid I of tube Vs positive and decreasing in potential. The half of tube Vs comprising anode 3 and cathode 4 is poled in the wrong direction and no current passes through it. The negative diminishing voltage at cathode 6 of tube V4, however, finds a path through anode 5, cathode 8 of tube V to control grid 4 of tube Vs. In .this case resistor 2M acts as a shunt across cathodes 3 and 6 of tube V4.

Elements 4, 5 and 6 of tube Vs are normally biased to cut-off but as control grid 4 thereof becomes less negative, a point is reached at which the voltage at this grid is close enough to zero forcurrent to fiow. Tube Vs then opens up very rapidly, forming a negative pulse at anode 5 thereof and a positive pulse at anode 2 as mentioned above.

If the opposite direction for the voltage across cathodes 3 and 6 of tube V4 is assumed, the result is the same, that is, with the voltage at cathode 3 negative and diminishing, grid 4 of tube V6 becomes less negative through the circuit including resistor ZBI and the critical point is again reached at which the desired voltage pulses are formed precisely as for the case of opposite polarity above described. In this case the shunting circuit comprises resistor 282 and elements 3 and l of tube V5.

The action of the circuit just described can be briefly summarized as follows. Considering the voltage at grid I of tube V1 to be zero, then if the circuits are correctly adjusted and set up, the voltages from cathodes 3 and 6 of tube V4 to ground are equal. No current is being passed by either of the diodes of V5 and thus grids I and t of V6 are at equal potential with respect to ground. Because of resistor 28 3, the first half of the tube V6 is in a semi-cut-ofi condition. Now, any change of the voltage applied to grid I of tube V1 will cause the voltages at cathodes 3 and 6 to be unequal, and by virtue of this circuit no matter what the polarity of this change, grid I of V6 will become more positive and grid d of V6 will become more negative. Resistor 263 is in the circuit to reduce the eiiective gain, thus widening the base of the pulse.

Thus, at coincidence (zero voltage grid I of V1), plate 2 of V6 assumes its most positive position. At any point removed from coincidence, it is more negative. The amount it can go negative is determined only by the resistors and circuits of this tube. This will, however, reach a finite limit. The amount of movement of grid I of tube V1 required for plate 2 of V6 to reach its finite limit is determined solely by the amplifier characteristics of the total network V1 to V6, that is by the amount of gain.

Terminals 214 and 216 are, of course, the output terminals to which connections are made from circuits to be controlled by the pulses generated. Circuits requiring a positive control pulse are, of course, connected to terminal 2'14 and those requiring a negative control pulse are obviously connected to terminal 216. A primary purpose of the over-all circuit employed for illustrative purposes is to provide a circuit which will generate control pulses each time that the highly directive beam of the exploring or scanning antenna passes through a particular azimuth angle Whether the antenna is rotated in one direction continuously or oscillated back and forth through an are including the particular azimuth angle. Pulses thus obtained can be employed to provide azimuth marks on the indicator associated with 8 radar system (usually one or more cathode-ray oscilloscopes are employed with each radar system) or they can be employed to operate a cirsuit to light a signal lamp or similar warning device.

Obviously, the principles of the invention can also be employed in many other systems to proits spirit and scope.

vide indications or warning signals whenever a movable element passes any particular selected point in its normally traversed path or orbit. Numerous other arrangements can therefore manifestly be readily devised by those skilled in the art to operate in accordance with the principles of the invention without departing from The scope of the invention is defined in the following claims.

What is claimed is:

1. An index control pulse generating system for generating control pulses of predetermined character each time that a rotating or oscillating member passes through any particular selected point within the path or orbit of its motion, which comprises in combination, a first variable voltage dividing device, a first direct current voltsource, one terminal of said device and the positive terminal of said source being grounded, the other terminal of said device being connected to the ungrounded terminal of said source, a mechanical coupling between said device and the rotatin or oscillating member to vary the output voltage of said device continuously as said member moves, a second variable voltage dividing device, a second direct current voltage source, one terminal of said device and the negative terminal of saidsecond voltage source being grounded, the other terminal of said device being connected to the ungrounded terminal of said source, manual means for adjusting the voltage output from said second voltage vaiying device, to any value within the range of variation of the first stated voltage varying device, a summing amplifier, electrical connections between the outputs of said first and second voltage varying devices and the input of said summing amplifier, a phase-inverter vacuum tube circuit providing a push-pull output, the input of said circuit being connected to the output of said summing amplifier, a push-pull cathode follower vacuum tube circuit, the input of said last-mentioned circuit being connected to the output of said phase-inverter circuit, a pulse generating vacuum tube circuit comprising at least a double triode vacuum tube circuit, or its equivalent, biased to produce a negative pulse at one anode and a positive pulse at the other anode when the input voltage thereto passes through zero and at least a double diode rectifying vacuum tube circuit, or its equivalent, said rectifying circuit being cooperatively connected between the output of said push-pull cathode follower circuit and the input of said pulse generating circuit whereby said last-mentioned circuit provides a negative index pulse at one anode and a positive index pulse at the other anode whenever the output of said summing amplifier passes through zero.

2. An index generating circuit for use in a system which performs a recurrent and reversible sweeping action and in which it is desired to obtain an index pulse at a predetermined adjustable point in the sweeping action for both directions thereof, the combination which comprises a first means providing a first voltage which increases uniformly throughout the sweeping action when in one direction and decreases uniformly throughout the same sweeping action when performed in the reverse direction, said first voltage having a particular discrete value for each point in the sweeping action irrespective of the direction of sweep, a second means providing a second voltage adjustable to equal the value of said first voltage but of opposite polarity at any selected point in the sweeping action and a third means cooperatively associated with said first and said second means and responsive to said first and said second voltages to provide electrical impulses of predetermined and invariable polarity whenever said first voltage passes through the value to which said second voltage is instantly adjusted, said third means comprising in combination a summing amplifier the input of said amplifier being connected to said first and said second means, a phase inverter vacuum tube circuit providing a push-pull output, the input of said phase inverter circuit being connected to the output of said summing amplifier, a push-pull cathode follower vacuum tube circuit, the input of said lastmentioned circuit being connected to the output of said phase inverter circuit, a pulse generating vacuum tube circuit comprising at least a double triode vacuum tube circuit biased to produce a negative pulse at one anode and a positive pulse at the other anode when the input voltage thereto passes through zero and at least a double diode rectifying vacuum tube circuit, said rectifying circuit being cooperatively connected between the output of said push-pull cathode follower circuit and the input of said pulse generating circuit.

3. In an electrical system, a first voltage source providing a first voltage of predetermined polarity which varies between particular limiting values, a second voltage source providing a second voltage of the opposite polarity to said first voltage the value of which is adjustable to any discrete value within the said limiting values and means including a summing amplifier cooperatively associated with and responsive to said first and said second voltage sources to provide an electrical impulse of a predetermined and invariable polarity at instants during which said first voltage passes in either direction through the value to which said second voltage is adjusted said laststated means also including in tandem relation with said summing amplifier a phase inverter vacuum tube circuit, a cathode follower circuit, a rectifying circuit and a pulse generating circuit. 4. An index pulse generating circuit for use in a system which performs a recurrent and reversible sweeping action and in which it is desired to obtain an index pulse at a predetermined adjustable point in the sweeping action for both directions thereof, the combination which comprises a first means providing a first voltage which increases uniformly throughout the sweeping action when in one direction and decreases uniformly throughout the same sweeping action when performed in the reverse direction, said first voltage having a particular discrete value for each point in the sweep irrespective of the direction of sweep, a second means providing a second voltage adjustable over a range of voltages of opposite polarity to the range of voltages swept by said first means, said second range of voltages having a definite known relation to said first range of voltages, a summing amplifier, the input of said amplifier electrically connecting to said first and said second voltage providing means, the input circuits of said amplifier being proportioned and arranged to weight the voltage from said second means in accordance with said definite known relation between said voltage ranges, a phase inverter circuit, a push-pull cathode follower circuit, a rectifying circuit and a pulse generating circuit, said summing amplifier, phase inverter, cathode follower, rectifying and pulse generating circuits being connected electrically in tandem and providing a pulse of predetermined character whenever said first and said second means provide predetermined voltages proportioned in accordance with said definite known relation.

WILBUR L. GAINES.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 2,266,401 Reeves Dec. 16, 1941 2,321,605 Keinath June 15, 1943 

